The invention relates to a method of and to an apparatus for manipulating sheets of paper or the like, especially for wrapping printed and folded sheets in a bookbinding, newspaper printing or like plant. More particularly, the invention relates to improvements in a method of and in an apparatus for confining individual sheets or groups of overlapping sheets in foils of plastic material or the like. Still more particularly, the invention relates to improvements in a method of and in an apparatus for confining groups of sheets between pairs of panels consisting of a light-transmitting or opaque weldable plastic material, especially between pairs of panels which form loops with bights ready to receive the leaders of successive groups of overlapping sheets.
It is often advisable and/or necessary to confine groups of sheets in transparent or translucent foils of synthetic plastic material. The wrapping machines which employ webs of such plastic material are often designed to loop a single web or strip of plastic material or to repeatedly unite the leaders of two webs so as to form a loop which is ready to receive the foremost group of a series of groups of overlapping sheets and to be thereupon converted into an envelope which preferably completely confines and seals a group from all sides.
A drawback of presently known wrapping machines of the just outlined character is that they cannot confine successive sheets or groups of sheets at the rate at which the sheets issue from a highspeed printing machine for the making of brochures, pamphlets, newspapers and similar products. The reason is that the wrapping machines (wherein groups of overlapping sheets are normally compressed, compacted or otherwise flattened prior to draping) operate intermittently whereas a printing machine can turn out continuously an extraordinarily large number of printed sheets or the like per unit of time. Therefore, if the printed products are to be wrapped in an intermittently wrapping machine, the printing machine which supplies the products must be operated at less than rated speed.